1. Field of the Invention
The present invention relates to a method and an apparatus for measuring contamination of a semiconductor substrate. More particularly, the present invention relates to a method and an apparatus for selectively measuring a metal contamination of a substrate, wherein the substrate has patterns formed on a surface thereof.
2. Description of the Related Art
As a design rule of a semiconductor device is reduced, contamination of a substrate caused by various sources becomes more serious because a failure of the semiconductor device may be generally induced by contamination of the substrate. Thus, a method for monitoring a level of contamination of the substrate has been emphasized. Particularly, an interior and a surface of a semiconductor substrate including silicon may be easily contaminated by undesirable metal sources, such as iron, copper, aluminum and the like, during semiconductor manufacturing processes. These metal contamination sources may be rapidly diffused into the semiconductor substrate including silicon thereby causing a failure of the semiconductor device.
In general, there are two methods for measuring contamination of a semiconductor substrate caused by metal sources. A first method is a direct measuring method, such as a secondary ion mass spectrometric method. A second method is an indirect measuring method, such as a surface photo voltage (SPV) measurement method. In the SPV measurement method, the contamination of the substrate caused by metal sources can be indirectly measured by detecting diffusion distances and life times of minority carriers.
The SPV measurement method has been widely utilized because this method does not require an additional sample to measure contamination and the level of contamination can be measured with respect to an entire surface of the semiconductor substrate.
Disadvantageously, the SPV measurement method may not be performed on a semiconductor substrate including patterns formed thereon to measure a level of contamination of the semiconductor substrate. When a surface photo voltage is directly measured on a semiconductor substrate where the patterns are positioned, light incident on the substrate for measuring the surface photo voltage may be scattered by the patterns on the substrate. As result, an induced current induced from the surface of the substrate may be distorted such that the surface photo voltage may not be precisely measured. To overcome this disadvantage, an additional substrate that does not include the patterns is employed to measure the level of contamination of the substrate. Therefore, the SPV measurement method may not be directly employed for a substrate including patterns formed through the semiconductor manufacturing processes.
Further, to measure the level of the contamination over the entire surface of the substrate, the surface photo voltages are measured at previously set portions of a front surface of the substrate being monitored. Obtained data of the contamination of the substrate being monitored are outputted with respect to each portion of the substrate as a map shape using the measured surface photo voltages. However, when a contamination occurs locally at a very small portion of the substrate that includes patterns, that contamination of the substrate may not be detected because measurements taken from the previously set portions of the substrate may not represent the portions of the substrate where the contamination occurred.